"It never occurred to me that it might be a joke," she recalled. "I knew that Albert Einstein's brain had been preserved and that it was somewhere where someone was looking after it."

For 40 years, Harvey, a retired pathologist from Princeton, N.J., had been the quixotic custodian of the 20th century's most famous brain.

In 1955, he had conducted a routine autopsy of Einstein after the 76-year-old physicist died at Princeton Hospital. The remains were to be cremated. Harvey, however, decided to preserve the organ responsible for the theory of relativity and the principle of the atomic bomb.

It was not such an unusual thing to do. Einstein's ophthalmologist had removed the scientist's eyeballs and put them in a safe-deposit box. Earlier acquisitive anatomists had preserved Galileo's finger, Haydn's head and Napoleon's penis.

For Harvey, however, more than morbid curiosity was at work. He believed that the slippery worms of Einstein's brain tissue, pickled in warm formalin, embodied some clue to the mystery of intelligence. He held on to that hope through 40 years of indecision.

Eventually, it led the soft-spoken Quaker to Witelson, a raven-haired Canadian psychologist with a taste for black leather and red showgirl nails.

She had brains, dozens of them — the largest collection of normal brains in the world.

When Witelson began acquiring human brains, sex was the last thing on her mind.

Inside her walk-in refrigerator at McMaster University here in Ontario, her collection filled three walls of metal shelves. The 125 putty-colored specimens sat in frosted jars and snap-top plastic tubs like quarts of boiled shrimp and wedges of cheese.

Every one posed a riddle that had shaped her research for 30 years: How does the structure of the brain influence intelligence?

A professor of psychiatry and neuroscience, Witelson grappled with such a fundamental mystery by studying a somewhat smaller one: why certain abilities develop on one side of the brain rather than the other.

The two hemispheres of the brain are almost symmetrical physically but can seem to be separate minds when it comes to awareness and mental processing. They even have different problem-solving styles, researchers report. Yet they work together seamlessly to produce a single mind.

By 1977, Witelson was trying to learn why language skills developed on the left side of the brain for all right-handers but on the right side for many left-handers.

To compare the two sides, she needed normal brains — more than anyone had gathered before.

For 10 years, she worked through a network of doctors and nurses, hoping to persuade terminal cancer patients to make a last contribution to medicine. Her research was funded by the U.S. National Institutes of Health.